The invention relates to a device for injection moulding insulating disks onto the inner conductor of high-frequency coaxial cables comprising a turret which is rotatable about its axis and at whose circumference are located mold cavities which are radially arranged and which are provided with radially outwards extending moulding ducts for forming the insulating disks, wherein the mold cavities, through the centers of which the inner conductor passes, can be opened and closed, said device further comprising a system for feeding the moulding material to the mold cavities and comprising an injection nozzle which, injection nozzle is directed towards the outer surface of the turret, and a separation member for separating the strip of moulding material, formed during moulding on the circumference of the turret, from the insulating disks.
Such a device is known already from U.S. Pat. No. 4,133,622 the contents of which are hereby incorporated by reference. In the method of this patent inner conductor provided with the insulating disks leaves the turret in stretched condition, while the individual insulating disks are still interconnected by the strip of moulding material formed during injection moulding on the outer surface. Due to the fact that the strip of moulding material is formed at a radius which is larger than that along which the inner conductor extends, dislocations of the strip of moulding material occur after stretching of the inner conductor because of the excess length of this strip so that the insulating disks are displaced from their desired position by unilaterally applied shearing and bending forces of different values and are detached.
This effect, which has a considerable unfavourable influence on the high-frequency cable is the more strongly pronounced as the insulating disks are cured to a lesser extent. Since in the known device, the size of the injection nozzle opening substantially corresponds to the diameter of the moulding ducts, the moulded insulating disks cannot be compressed within the required hold-on pressure time, especially at high manufacturing speeds, so that they are cured only incompletely or do not enclose the inner conductor to the required extent and thus are loosened more readily upon application of external forces.
At higher manufacturing speeds, there is the disadvantage that the insulating disks, before they leave the turret, cannot be cooled sufficiently rapidly so that their adherence to the inner conductor is further reduced. Moreover, at higher speeds there is a risk that the cavities for forming the insulating disks are filled only incompletely with moulding material because the extruder screw makes available the moulding material, which is substantially not compressible, in the quantity which is required between two moulding ducts as a moulding material strip, and during the comparatively short time in which the injection nozzle and sprue overlap each other, only a part of the moulding mass is allowed to enter the mold cavities because otherwise the strip of moulding material serving as a lubricating film would be interrupted. In the absence of a sufficient moulding pressure, also in this case no fixed seat of the isolating disks on the inner conductor will be possible.